1. Field of the Invention
The present invention relates to a cleaning apparatus for an image forming apparatus utilizing an electrophotographic process such as an electrophotographic copying apparatus or an electrophotographic printer.
2. Related Background Art
Recently, a composite apparatus having functions of all the output terminals for a copying apparatus, a printer, a facsimile and the like is widely accepted in the market. An image forming apparatus utilizing an electrophotographic process is widely accepted as an output terminal adaptable to a network, but a duty cycle of a main body of the apparatus is pointed out as a major issue to be solved.
A duty cycle means a limit print number for which the main body can be operated without a maintenance operation by a service personnel, and one of the largest issues for such duty cycle is a service life of an image bearing member. Also from the ecological point of view, most important issues are an elimination of discarded materials, a reduction in consumables, an extended service life of consumables and an increase in the reliability.
On the other hand, a transition from the prior analog apparatus to a digital configuration is showing a remarkable progress, and a reduction of the cost of a digital apparatus to that of an analog apparatus or lower is also another issue. Furthermore, monochromatic copying apparatus and printer have been principally employed, but full-color originals and output files are showing a rapid increase also in the office market. Thus, there are being desired not only a digital apparatus equivalent to the analog apparatus in cost but also a full-color printer equivalent to the monochromatic apparatus in the cost of the main body and in the running cost, and, for such purposes, a technology capable of drastically reducing TCO (total costs from the standpoint of a user) is desired.
In an image forming apparatus utilizing an electrophotographic process technology, in order to realize a full-color printer having an engine equivalent in cost to a monochromatic printer, there is conceived a technology of employing an intermediate transfer member and superposing images of four colors on the intermediate transfer member by a single photosensitive member. Also an intermediate transfer member constructed as a running belt member increases the freedom of layout in the main body of the printer, thereby enabling a compactization of the apparatus. Therefore, while the photosensitive member alone is an image bearing member in a monochromatic printer, the intermediate transfer member also becomes an image bearing member in a full-color printer, so that a surface cleaning operation is required in a wider area in order to use various image bearing members in repeated image formation cycles.
For cleaning a surface of the image bearing member, there is employed a method of contacting an edge of a cleaning blade, constituted of an elastic material such as rubber, with a surface of an image bearing member to be cleaned and scraping off residual toner adhering to such surface, thereby cleaning such member to be cleaned.
FIG. 2 shows an example of a known cleaning apparatus for cleaning an intermediate transfer member, in which a cleaning blade 19 of a cleaning apparatus is so positioned close as to contact an intermediate transfer belt 4 of a belt shape having an axis perpendicular to the plane of the drawing. Though not illustrated, a photosensitive member and a secondary transfer roller are provided along a periphery of the intermediate transfer belt 4.
Though not illustrated, the cleaning apparatus has a casing having an aperture in a direction toward the intermediate transfer belt 4, and, in the aperture of the casing, there is mounted an edge of the cleaning blade 19 formed for example by urethane rubber. An edge of the cleaning blade 19 is contacted with the intermediate transfer member 4 in a counter direction to a driving direction A thereof, and, a transfer residual toner, generated in an unillustrated secondary transfer portion, upon reaching the edge portion of the cleaning blade 19, is scraped off by the cleaning blade 19.
Also when the transfer residual toner, scraped off and remaining by the cleaning blade 19, is supplied again in a small amount to the edge portion of the cleaning blade 19 by the rotation of the intermediate transfer belt 4, the cleaning blade 19 is prevented from being turned up owing to a lowered friction by the presence of the powder of the transfer residual toner, whereby a satisfactorily stable cleaning performance can be obtained. The cleaning blade 19 is so set, depending on a thickness of a rubber material, a length (free length) of a front rubber portion and a contact pressure, as to achieve an improved toner eliminating ability and a prevention of the turning-up of the cleaning blade.
In order to more satisfactorily clean the transfer residual toner on the image bearing member, it is proposed, for example in Japanese Patent Application Laid-open No. S56-055979 to functionally select constituting materials, such as constituting the cleaning blade with plural layers, and employing a hard material in a portion of the cleaning blade coming into contact with the image bearing member.
In an image forming apparatus utilizing an electrophotographic process technology, because a discharge phenomenon is utilized for example in a charging step, substances such as ozone products adhere to the surface of the image bearing member such as a photosensitive member. Such phenomenon increases a friction between the cleaning blade and the cleaned surface, thereby resulting in a turning-up of the cleaning blade or a perturbation of image formation by a substance adhering to the surface of the image bearing member, thus leading to an image defect. It is therefore desirable that the cleaning blade is easily slidable. Also the cleaning function includes not only an eliminating function for the transfer residual toner remaining on the surface of the image bearing member, but also a function of polishing the cleaned surface. For this reason, a harder surface is preferred for the cleaning blade, but it is difficult to contact a hard material uniformly over a wide area. Therefore, in case of employing a hard cleaning blade for obtaining a long service life, there has been required a pressurizing method for precisely pressing such cleaning blade to the cleaned surface.
Also a technology of realizing a hard surface layer with a low friction by a progress in the rubber material is proposed for example in Japanese Patent Application Laid-open No. H04-212190.
This technology is based on coating a surface of a cleaning blade material with a resin containing lubricant particles. This technology realizes a stable contact state in a simple configuration by the flexibility and the adaptability of the rubber material, also avoids the turning-up of the cleaning blade by the lubricant particles and also provides a polishing function for the surface of the image bearing member by the hard surface layer.
In such configuration, however, because the resinous material is coated thinly on the surface of the cleaning blade, such coated portion may be abraded off or peeled off in a prolonged use, thereby restricting the service life of the cleaning blade.
Also a cleaning blade utilizing an ordinary urethane rubber, though showing a very high frictional coefficient, provides a low frictional coefficient in a three-component system including powder, in the presence of fine particles such as toner.
However the supply of such powder material varies for example by an image to be formed, so that the cleaning blade shows an unstable behavior in an actual contact portion. The polyurethane rubber shows a high abrasion resistance because it is not easily torn when a blade edge is strongly pulled in an eventually unstable friction state, and is not deteriorated by a repetition of such state.
On the other hand, a hard material such as a resinous material is, in comparison with a soft material such as a rubber material, stronger in a resistance against an external force such as an elongation or compression, but is smaller in a possible amount of elongation or contraction. Therefore, in case a cleaning blade is made harder only in a vicinity of a portion coming into contact with the image bearing member, a portion close to the surface of the cleaning blade cannot withstand a deformation by an elasticity of the entire cleaning blade, whereby the cleaning blade is abraded or broken to result in for example a chipping in the blade, thereby deteriorating the cleaning ability.
Also polyurethane rubber, commonly employed in the cleaning blade, is resistant to repeated deformation as long as physical properties are not changed, but the resinous material generally shows a deterioration such as a decrease in a tensile stress or a decrease in a breaking elongation, by repeated deformations.
While a longer service life for the image bearing member is being realized for example by an improvement in the abrasion resistance of the photosensitive member, the cleaning blade are now required to meet various functions and a longer service life is also essential for the cleaning blade itself.